Variability in developmental milestones and developmental delay in children with Williams syndrome

Williams syndrome (WS) results from damage (varying in extent between individuals) to chromosome 7. Symptoms include cardiovascular problems, 'elfin' faces, intellectual difficulties and hypersociability. Psychological studies have tended to be of small samples and have typically treated symptoms as uniform across individuals, though medical studies report considerable variability. The current study examines psychological and genetic characteristics of 78 children with WS seen at a single Greek clinic over a decade. The findings include first, that intellectual performance is related to level of genetic loss, but the same level of genetic loss produces different phenotypes across individuals. Second, attainment of key developmental milestones is delayed commensurate to level of genetic loss, though motor control is significantly delayed in all cases. The implications of these findings are examined. The study demonstrates the diversity of symptoms exhibited by children with WS, and indicates a need for caution when drawing conclusions from small sample studies of conditions such as WS.